All non-essential activity on the Murray River in South Australia has been banned as floodwaters continue to rise.
The ban includes boating, fishing and swimming with the restrictions in place from the Victorian border to Wellington, southeast of Adelaide.
It takes effect immediately and is expected to remain in place at least into January.
"This is a decision that hasn't been taken lightly," Premier Peter Malinauskas said on Tuesday.
"But unfortunately, as the waters continue to peak we're now at a point where we need to close the river."
There are exceptions to the prohibition with people requiring access to the river for work or visiting their properties able to do so and the supply of food and other provisions will also be allowed.
The premier said the ban had been imposed in the interests of public safety, to allow SA Power Networks to better manage electricity disconnections and to prevent damage to levee banks.
He said the decision was regrettable during the peak holiday period and the river would reopen as soon as possible.
"We don't want a situation where the river is closed for a moment too long. As soon as it is safe to reopen that will be undertaken taken," Mr Malinauskas said.
Police will work to educate the community about the new regulations but those who persistently breach the ban could face a fine of up to $10,000.
Enforcement will involve river and aerial patrols.
In other developments, Lake Bonney near Barmera has been hit with an algal bloom after being cut off from the Murray by a newly constructed levee to protect properties in the town.
State Emergency Service chief officer Chris Beattie said only part of the lake was affected and the levee would be removed as soon as possible after the river peaked, allowing for natural water flows to resume.
As water levels continue to rise, eight levees have suffered major failures so far with defects identified in about 50 more.
Of those three were causing most concern with engineers doing repairs.
Mr Beattie said none of the breaches had resulted in major issues for properties or other infrastructure but it was inevitable there would be more problems.
"A lot of these structures were originally built 50 or 60 years ago. In that context, we will see degradation," he said.
"Having said that the principal levees around the townships and critical infrastructure have had significant works undertaken by councils.
"They have been engineered to a good standard, to a contemporary standard. We've got high confidence in those levees being up to the task."
About 4000 properties across the length of the Murray in SA are expected to be inundated with more than 1100 flooded so far.
The high-water mark is likely to hit Renmark, near the Victorian border about Boxing Day and then reach Murray Bridge by January 17.
Daily peak flows are still forecast between 190 and 220 gigalitres but then expected to drop back to about 150 gigalitres by February, allowing clean-up work to begin.
